1. Field of the Invention
The present invention relates to a method and apparatus for curing foundry cores, and, in particular, a method and apparatus whereby a vaporized curing agent is introduced into a core mixture to harden a curable binder mixed with the foundry aggregate of the core.
2. Prior Art
Foundry cores or molds are made from sand or similar foundry aggregate which is held together in the desired shape by means of a binder. Generally, the process used to form the foundry core comprises mixing the foundry aggregate with the binder, forming the mixture into the desired shape, then treating the mixture so that the binder hardens sufficiently so that the core can be handled.
The efficiency and dimensional quality of the core is enhanced if the curing or hardening of the core is achieved in a minimum amount of time. It is also desirable to harden the core without heating the mixture, as this may cause the core to deform thereby losing dimensional accuracy.
Various methods have been employed in an attempt to cure rapidly the mixture of foundry aggregate and binder. These methods commonly employ an isocyanate or phenolic material as a binder and harden the mixture by introducing an amine, in particular triethylamine or dimethylethylamine, to the mixture either in the form of a gas or a fine mist. The amine acts as a catalyst to promote cross linking of the binder, thereby hardening the core mixture.
An example of such a process is disclosed in U.S. Pat. No. 3,888,293, which discloses the curing of a foundry core by the introduction of an amine vapor which is mixed with an inert gas carrier and blown into the core. A pool of liquid amine in a generating tank is heated to form amine vapor. Inert gas, such as nitrogen, is blown into the tank, mixes with the amine vapor, and the mixture exits the tank to pass through a surge tank where it is mixed with additional inert gas to form a vapor solution of a normally liquid amine in an inert carrier gas.
The vapor solution exiting the surge tank flows to a T-joint where it is entrained in an inert gas of low pressure and carried into the core where the outer portion of the core mixture is "flash cured". A second gasing occurs in which a high pressure stream of inert gas entrains the vapor solution and drives the vapor solution into the inerior portion of the core mixture. The core mixture is then purged by the introduction of a stream of shop air which drives the vapor solution from the core into a holding tank or air scrubber.
A disadvantage of this system is that it is necessary to control the concentration of the amine in the vapor solution by using a surge tank downstream of the generating tank. In addition, the generating tank must be large enough to hold a predetermined amount of liquid amine at all times during operation and provide a sufficient air space above the liquid amine to allow mixing of the amine with the inert gas so that droplets of liquid amine are not carried with the mixture through the system. Additional equipment would be required to drain the generating tank and provide for the cooling off of the liquid amine when the system is shut down, further complicating the overall operation.
In U.S. Pat. No. 4,051,886, a foundry mold curing system is disclosed in which an inert gas, such as carbon dioxide, is bubbled through a quantity of liquid amine held in a tank so that the carbon dioxide becomes a vapor saturated with liquid amine. The resulting saturated vapor is then blown into the core box to cure the core mixture. Again, a large tank is required to hold the liquid amine and permit a large air space to remain above the liquid. This patent teaches away from heating the liquid amine to form a gas. Instead, it is suggested that the liquid amine be maintained at ambient temperature so that the saturated vapor does not condense in the lines leading to the core box.
A disadvantage of this system is that the velocity of the carbon dioxide through the liquid amine must be slow so that a proper amount of amine may be absorbed by the carbon dioxide gas. In addition, a large tank is required which would add to the expense of the system and the difficulty in fabrication of the components. Finally, there is no means for regulating the concentration of the amine absorbed by the carbon dioxide or regulating the flow of the carbon dioxide mixture other than an air operated gassing valve. As with the aforementioned system, liquid amine must be drained from the holding tank when the system is shut down.
Accordingly, the need exists for a more efficient system for introducing a curing agent, such as amine, into a core mixture.